The nucleocapsid protein p7 is required for the maturation and packaging of HIV-1 RNA. The protein (55 residues) contains two zinc fingers and a single Trp residue that is involved in nucleic acid binding through stacking interactions with nucleobases. We are in the process of characterizing the lifetime and dynamic anisotropy properties of free NCP p7, metalated with various divalent ions (Zn^2+, Cd^2+, Co^2+) and in its complexes with DNA and Rna oligonucleotides. E.coli SSB and gene 5 proteins are amongst the best characterized non-sequence specific nucleic acid binding proteins from the point of view of their structure, function and physical chemistry. While wild type E.coli SSB has 4 Trp residues amongst its primary sequence, gene 5 protein is devoid of Trp residues. We have prepared point mutations of E.coli SSB that have one Trp at a time substituted by a non-emitting residue, and show that it is possible to resolve the spectral properties of the individual Trp residues through a global analysis of the spectra and dynamic fluorescence response of a series of point-mutated SSBs (see Biophys. J. 64, A178 (1993), and SPIE Proc. 2137, in press (1994)). The study of triple point-mutated SSBs that retain only one Trp residue at a time is currently underway. We have also engineered mutants of gene 5 protein that contain a single Trp residue at the position of either the dimer interface or the RNA-protein interface. Perturbations of the Trp fluorophores upon oligonucleotide binding are being investigated to provide a model for the interaction of intercalating aromatic residues with nucleic acid lattices.